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| #1144150 (Received by flhurricane at: 4:54 PM 17.Jul.2023) TCDAT5 Tropical Depression Don Discussion Number 15 NWS National Hurricane Center Miami FL AL052023 900 PM GMT Mon Jul 17 2023 GOES-16 visible imagery shows that Don is comprised of multiple low-level swirls rotating around the larger circulation, which is better defined than you might think at the surface based on earlier scatterometer data. Overall, the system is not well organized due to persistent shear, dry air and marginal instability, with only a distant burst of convection well east of the center. There has been no change with the latest satellite classifications, so the initial wind speed remains 30 kt. The environment around Don is forecast to become more conducive for gradual intensification in a couple of days when the cyclone moves over warmer waters with light-to-moderate shear, tempered by plenty of mid-level dry air. Surprisingly, many of the recent regional hurricane models show a hurricane forming over 24-25C waters in several days time, which is hard to believe given the seemingly marginal large-scale conditions. Additionally, Don will have to cross its own cool wake in 4-5 days, which isn`t well accounted for in the models yet. The new forecast is bumped up at day 5 but remains below the model consensus. Don has turned southeastward at about 12 kt, in the process of undergoing a large anticyclonic loop over the central Atlantic due to a blocking ridge to its north. The depression should begin to gain latitude again late on Wednesday as the blocking ridge slides eastward, and eventually Don should turn northwestward by the end of the forecast period. The biggest question remains how sharp of a turn will occur late this week, with the ECMWF suite insisting on a faster northward motion by the weekend, well east of the other guidance. An examination of those fields suggests that it doesn`t vertically redevelop Don as much as the rest of the guidance, resulting in the cyclone not responding to the upper-level southeasterly flow, and instead turning more quickly northward. Since the new intensity forecast remains on the lower side of the guidance envelope, the new NHC track forecast will also stay east of the model consensus, not too different from the last prediction. FORECAST POSITIONS AND MAX WINDS INIT 17/2100Z 38.1N 41.6W 30 KT 35 MPH 12H 18/0600Z 37.1N 40.2W 30 KT 35 MPH 24H 18/1800Z 35.4N 39.4W 30 KT 35 MPH 36H 19/0600Z 34.3N 39.5W 30 KT 35 MPH 48H 19/1800Z 33.6N 40.5W 35 KT 40 MPH 60H 20/0600Z 33.8N 41.5W 35 KT 40 MPH 72H 20/1800Z 34.4N 43.0W 40 KT 45 MPH 96H 21/1800Z 36.7N 46.8W 45 KT 50 MPH 120H 22/1800Z 40.5N 50.0W 45 KT 50 MPH $$ Forecaster Blake |
